Synchronous induction motor having a segmented



P. F. BAUER ET AL NDUCTION MOTOR HAVING A SEGMENTED ROTOR AND SQUIRREL CAGE WINDING Filed Dec. 15, 1954 2 Sheets-Sheet l P. F. BAUER ErAL 2,733,362 SYNCHRONOUS INDUCTION MOTOR HAVING A SEGMENTED ROTOR AND SQUIRREL CAGE WINDING Filed Deo. 13, 1954 2 Sheets-Sheet 2 United States Patent O SYNCHRONOUS INDUCTION MOTOR HAVING A SEGMENTED ROTR AND SQUIRREL CAGE WINDING 6 Claims. (Cl. S10- 162) This invention relates generally to an improved synchronous induction motor. More specifically this invention relates to a synchronous induction motor having a rotor construction resulting in improved operating characteristics for the motor.

Reluctance motors known motors used deep slots in the flux path in the rotor.

acteristics of any reluctance motor of the same rating used in the prior art. factor, eiiiciency, The improved combination of operating characteristics in a much smaller frame than the frames used in the art today on reluctance motors of the same rating.

This small frame plus the use of slots on the rotor today.

Another object or" this invention is to provide an improved .synchronous induction motor having a combination of operating characteristics namely pull-out torque, power factor superior to a combination of like characteristics of a prior art reluctance motor of the same rating.

Objects and advantages other than those set forth above will be apparent from the following description when read in connection with the accompanying drawings, in which:

sectional view bodiment of the motor taken in a direct axis flux path;

Fig. 2 is a cross sectional View of the motor of Fig. l with the rotor in a diierent position to show the quadrature axis linx path;

Fig. 3 is a pictorial view of the rotor with part of the end disk and end ring removed;

Fig. 4 is a graph showing how the power factor, eiliciency and pull-out torque vary with the changing pole embrace of the rotor;

Fig. 5 is a view of a modilied form of tion which is nonsegmented;

Fig. 6 is a view of a modified form of a rotor lamination in which the segments are connected at the outer edge of the radial slots; and

Fig. 7 is a view of a modified form of a rotor lamination in which the segments are connected at the inner edge of the radial slots.

As shown in the a rotor 1aminamounted.

The rotor 12 consists of a cylindrical magnetic core i5' preferably laminated which is divided into a plurality of circumferentiaily spaced segments 16 by radial dividing slots 17 and a bore E3. Nonsegmented laminations as shown in Fig. 5 may be interspers d periodically in the laminated magnetic core 15 to aid in securing the segments 16 together. The dividing slots i7 extend from the bore 1S to the periphery of the core and may be lled with any suitable nonmagnetic electrically conducting material. But preferably as shown the radial dividing slots E7 are with nonmagnetic spacers connected at each end of 21 of brass or other metallic substance. rThe shaft 13 may be made of magnetic or nonmagnetic material such as stainless steel. lf the shaft 13 is made of magnetic material then a nonmagnetic sleeve 22 preferably of brass is fitted between the shaft 13 and the bore 18 of the iagnetic core 15 to magsegments 16 from each other. An axially extending groove 23 of segment 16. Adjacent grooves 23 dene salient poles 30 therebetween that and the axial grooves electrically conducting 23 are filled nect the nonmagnetic spacers 20. Fan blades 3S may be die cast integrally with the rings 36. The winding 37 causes the motor lil to have the good starting characteristics of an induction rnotor. Also the motor with this winding 37 has good synchronous characteristics.

The best method of making this rotor l?. is to lill the dividing slots i7, winding slots 26 and axial grooves 23 with the same nonmagnetic electrically conducting material, preferably aluminum. Then the rotor can be die cast in a single operation with the aluminum disposed around the laminated core segments i6 to form a cylindrical rotor thereby reducing to a minimum the windage losses of the motor.

For high speed operation of the motor the rotor l2 be secured together with nonmagnetic bands 39 and the segments 16 may be secured to the shaft i3 by nonmagnetic bolts 4t).

This motor is designed to give a high pull-out torque while the power factor and efficiency remain near their respective maximums. This is illustrated by the graph in Fig'. 4 in which the pull-out torque di, efficiency 42 and power factor d3 are plotted against the percent pole embrace of the rotor. The pull-out torque of the motor is a function of the direct axis reactance and the quadrature axis reactance of the magnetic circuit. The pull-out torque (l). O.) is proportional to a constant (It) times the difference between the reciprocal of the quadrature axis reactance (xq) and the reciprocal of the direct axis rcactance (xa):

To get a maximum pull-out torque the quadrature axis reactance must be reduced to a minimum while maintaining the direct axis reactance near its maximum. The reactance is proportional to the flux. Therefore to approach a minimum quadrature axis reactance quadrature axis ux must be reduced to a minimum. The quadrature axis flux of a rotor can be reduced by increasing the reluctance in the rotor llux path. The axial grooves 23 and radial dividing slots 17 in this rotor l2 increase the reluctance in the quadrature axis flux path and therefore decrease the quadrature axis flux. Hence the quadrature axis reactance is decreased. The direct axis flux is not materially affected by either the dividing slots 17 or the axial grooves Z3. Therefore the direct axis reactance remains about the same.

Because of the axial grooves 23 and dividing slots i7 in the rotor l2, the difference between the direct axis reactance and the quadrature axis reactance of the motor is increased. Hence the pull-out torque is increased.

The circumferential length of the axial grooves 23 is chosen so that the motor runs at near its maximum power factor and elliciency and still has a high pull-out torque. ln this rotor l2 it is necessary to malte the circumferential length of the axial grooves 23 ecual to 45% to 55% of the i circumferential length of the segments le to effect a synchronous induction motor with the combination of operating characteristics necessary for successful commercial operation.

ln the modified lamination illustrated in Fig. 6, the segments lo are joined at the outer end of Ithe dividing slot 44 by magnetically saturable bridges 45. Such an arrangement permits the laminations to be made in one piece which increases the mechanical strength of the rotor but does not materially affect the operating characteristics of the motor.

ln the modified lamination illustrated in Fig. 7, the segments il@ are joined at the end of the dividing slot i adjacent the shaft by magnetically saturable bridges d'7. ln this modification the dividing slot flares as it approaches the magnetically saturable bridge 47 thereby increasing the reluctance across the dividing slot de, to4 compensate for the decrease in reluctance duc to the magnetically saturableA bridge i7 across the dividing slot 46. By flaring the dividing slot 46 as it approaches the bore of the rotor, the length of the bridge i7 across the dividing slot at the bore of the rotor is increased. There is greater reluctance through the long narrow bridge 47 connecting the segments by bridging the flared radial slot than there would be through a shorter bridge that would bridge a radial slot that is not ared. Hence the reluctance across the dividing slot is further increased due to the use of the flared dividing slot rather than a straight dividing slot. A lamination having segments that are connected together by bridges can be made in one piece and such a structure gives the rotor greater mechanical strength.

Although but two embodiments have been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

lt is claimed and desired to secure by Letters Patent:

l. A synchronous induction motor comprising a stator, a rotor rotatable relatively to said stator, said rotor comprising a cylindrical magnetic core having a plurality of circumferentially spaced segments separated by radial dividing slots, said segments having axially extending winding slots,v the cylindrical surface of each of said segments having an axially extending groove or" uniform depth substantially equal to the depth of said winding slots, the circumferential length of said groove being substantially equal to 50% of the circumferential length o f said segment, said grooves and slots being filled with a uonmaguetic electrically conducting material and interconnected with each other at the ends of the rotor to form a cylindrical rotor with a squirrel cage winding.

2. A synchronous induction motor comprising a stator, a rotor rotatable relatively to said stator, said rotor comprising a cylindrical magnetic core having a plurality of segments separated by radial dividing slots, the cylindrical surface of each of said segments having salient portions separated by an axially extending groove symmetrical with respect to the quadrature axis and of uniform depth sufficient to substantially minimize the quadrature axis flux, the circumferential length of said groove being to 55% of the circumferential length of said segment, axially extending winding slots in the said salient portions of said segments, said grooves and slots being filled with a nonmagnetic electrically conducting material and interconnected with each other at the ends of the rotor to form a cylindrical rotor with a squirrel cage winding.

3. A synchronous induction motor comprising a stator, a rotor rotatable relatively to said stator, said rotor comprising a cylindrical magnetic core, said core being divided into segments by radial dividing slots and a bore, said dividing slots extending from the bore to the periphery of said core to separate said segments from each other, said segments having axially extending winding slots, a shaft on which said rotor is mounted, a sleeve of nonmagnetic material fitted between said shaft and said bore to magnetically isolate said shaft from said segments, the cylindrical surface of each of said segments having an axially extending groove of uniform depth equal to the depth of said winding slots, the circumferential length of said groove being substantially equal to of the circumferential length of said segment, said grooves and slots being filled with a nonmagnetic electrically conducting material and interconnected with each other at they ends of the rotor to form a cylindrical rotor with a squirrel cage Winding.

4. A synchronous induction motor comprising a stator, a rotor rotatable relatively to said stator, said rotor comprising a cylindrical magnetic core, said core being divided into segments by radial dividing slots and a bore, said dividing slots extending from the bore to the periphery of said core to separate said segments from each other, said segments having axially extending winding slots, a. shaft on which said rotor is mounted, a sleeve of nonmagnetic material fitted between said shaft and said bore to magnetically isolate said shaft from said seginterconnecting said bars at the ends of the rotor to form ments, the cylindrical surface of each of said segments a cylindrical rotor with a squirrel cage winding. having an axially extending groove symmetrical with 6. Asynchronous induction motor comprising a stator, respect to the quadrature axis and of uniform depth sufa rotor rotatable relatively to said stator, said rotor comlicient to substantially minimize the quadrature axis flux, prising a cylindrical magnetic core, said core being dithe circumferential length of said groove being 45% to vided into segments by radial dividing slots and a bore, 55% of the circumferential length of said segment, said each of said dividing slots extending from the periphery grooves and slots being filled with a nonrnagnetic elecof said core to said bore and daring out as said dividing trically conducting material and interconnected with slot approaches said bore, magnetically saturable bridges each other at the ends of the rotor to form a cylindrical for connecting said segments, each et said bridges exrotor with a squirrel cage winding. tending across the llared portion of one of said dividing 5. A synchronous induction motor comprising a stator, slots adjacent said bore, nonmagnetic spacers disposed in a rotor rotatable relatively to said stator, said rotor comand partially iilling said dividing slots, said segments prising a cylindrical magnetic core, said core being dihaving axially extending Winding slots, a shaft on which vided into segments by radial dividing slots and a bere, ysaid rotor is mounted, a nonmagnetic sleeve iitted besaid dividing slots extending from said bore to the petween sai-:l shaft and said bore to magnetically isolate riphery of said core to separate said segments from each said shaft from said segments, the outer cylindrical surother, brass spacers disposed in and partially filling said face of each of said segments having an axially extending slots, said segments having axially extending winding groove of uniform depth equal to tne depth of said axially slots, a shaft on which said rotor is mounted, a brasa extending winding slots and symmetrically positioned sleeve fitted between said shaft and said bore to magwith respect to the quadrature axis to substantially reduce netically isolate said shaft from said segments, the cylinthe quadrature axis iiux thereby rendering the quadrature drical surface of each of said segments having an axially axis reactance to a minimum, the circumferential length extending groove of uniform depth equal to the depth oi of said groove being 45% to 55% of the circumferential said axially extending Winding slots and symmetrically length of said segment, sai grooves and slots being iilled positioned with respect to the quadrature axis to subwith bars of nonmagnetic electrically conducting matestantially reduce the quadrature axis flux thereby renderrial, and conductive rings intel connectmv said bars at the ing the quadrature axis reactance to a minimum, the ends of the rotor to form a cylindrical rotor with a circumferential length of said groove being 45% to 55% squirrel cage winding. of the circumferential length of said segment, said grooves and slots being lled with bars of nonmagnetic No references cited.

electrically conducting material, and conductive rings 

